High Temperature Chloride Corrosion Resistant NiCrTiAlSi/La2O3 Coating at Flue Gas Side of Waste Incineration Power Generating Boiler and Preparation Method Thereof

ABSTRACT

Provided are a high temperature and chloride corrosion resistant NiCrTiAlSi/La2O3 coating at a flue gas side of a waste incineration power generating boiler and a preparation method thereof. The method comprises the following steps: (1) preparing a composite powder; (2) uniformly grinding the composite powder to obtain a spherical composite powder, then drying the spherical composite powder; (3) cleaning and roughening a surface of a substrate; (4) using a thermal spraying technique to spray a primer layer on a heating surface; (5) using a thermal spraying technique to spray the spherical composite powder onto the primer layer; and (6) cooling. The coating obtained by the method comprises a composite coating spray-coated on a surface of the primer layer. A rare element in the form of La 2 O 3  is added to the coating to purify a grain boundary of the coating. The method strengthens the grain boundary and promotes the formation of an oxide film to alter the morphology of the coating, refine a crystal grain, and improve a high temperature and corrosion resistance and oxidation resistance of the coating.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No. PCT/CN2016/105686, filed on Nov. 14, 2016, which claims priority to Chinese Application No. 201610518201.X, filed on Jul. 1, 2016. The applications are incorporated herein by reference.

FIELD OF TECHNOLOGY

The present invention relates to the technical field of anticorrosive coating materials, in particular to a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler and a preparation method thereof.

BACKGROUND

Possessing such advantages of minimization, harmlessness and reclamation, waste incineration power generation is recognized as the best way to dispose waste. Compared with landfill disposal, waste incineration power generation has the advantages of small occupied space, easy site selection, short disposal time, dramatic minimization, complete harmlessness and capability of recovering waste heat from waste incineration, thereby becoming a waste disposal manner which is vigorously promoted domestically.

However, in solid wastes, since the concentration of chlorine is generally high (0.5%-2.0%), chlorination corrosion occurs during waste incineration. Due to its high activity, chlorine can react with almost all the metals at a high temperature, and the generated chloride has a low melting point and a high vapor pressure. Meanwhile, the presence of chlorine increases oxygen partial pressure required for forming a protective oxide film, such that the oxide film cracks and becomes loose and porous, thereby lowering its effective adhesion and protectiveness. Further, the corrosion of an incinerator is usually led by internal oxidation, and a selective corrosion preferentially occurs along a grain boundary inside the alloy. Therefore, during waste incineration, a serious problem of high temperature corrosion of materials will be undoubtedly a key issue which limits effective operation of a waste incinerator.

SUMMARY

An objective of the present invention is to overcome the disadvantages and shortcomings of the prior art, and provide a high temperature chloride corrosion resistant

NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler with a favorable corrosion resistance property at a high chloride environment of an incinerator and a preparation method thereof. The coating has favorable properties in resistance to high temperature erosion and high temperature chloride corrosion, and is especially applicable to heating surfaces of boilers made of carbon steel and other alloy steels.

The present invention is realized through the following technical solution: a method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler comprises the following steps:

(1) uniformly mixing Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder in proportion to obtain composite powder; (2) grinding evenly the composite powder obtained in the step (1) to obtain spherical composite powder and drying the spherical composite powder; (3) cleaning and roughening a surface of a heating surface of a waste incinerator; (4) adopting a thermal spraying technique to spray a primer layer on the surface of the heating surface; (5) adopting a thermal spraying technique to spray the spherical composite powder obtained in the step (2) on the primer layer in the step (4); and (6) cooling to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

Compared with the prior art, as to the method for preparing the high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention, an Inconel625-NiCrTiAlSi/La₂O₃ composite coating is sprayed on the surface of the primer layer; the adding of a rare element La₂O₃ can purify a grain boundary of the coating in the coating, thereby strengthening the grain boundary, promoting formation of an oxide film, changing the morphology of the coating, refining grains, and improving high temperature corrosion resistance and oxidation resistance of the coating. Moreover, the composite coating composed of Inconel625 alloy and NiCrTiAlSi/La₂O₃ alloy possesses the functions of multiple alloy coatings, thereby further improving capability of resistance to high temperature erosion of the boiler, prolonging service life of the waste incinerator, and saving cost.

Further, the NiCrTiAlSi/La₂O₃ alloy powder is composed of the following components in mass percentage: 80-85% of Ni, 5-8% of Cr, 3-8% of Ti, 3-8% of Al, 1-3% of Si and 2-4% of La₂O₃.

Further, in the step (4), the primer layer is a NiAl alloy layer.

Further, in the step (1), a mass percentage of the Inconel625 alloy powder to the NiCrTiAlSi/La₂O₃ alloy powder is (85%-90%):(10%-15%).

Further, in the step (4), the primer layer has a spraying thickness of 80-100 μm; and in the step (5), the spherical composite powder has a spraying thickness of 0.3-0.5 mm

Further, the spherical composite powder obtained in the step (2) has a particle size of 25-53 μm, and the spherical composite powder is obtained through ball milling the composite powder obtained in the step (1).

Further, the thermal spraying technique in the step (4) and step (5) is a supersonic flame spraying technique or a supersonic plasma spraying technique.

Further, technical parameters of the spraying technique in the step (4) and step (5) are as follows: a pressure of fuel gas propane is 0.35-0.45 MPa, a flow of combustion-supporting gas oxygen is 1600-1800 SCFH, a flow of kerosene is 5-7 GPH, a flow of carrier gas is 20-25 SCFH, a powder feed rate is 50-70 g/min, a gun distance is 300-400 mm, and a linear velocity is 400-600 mm/s.

Further, in the step (4), the primer layer is sprayed for 4 times; and in the step (5), the spherical composite powder is sprayed for 12 times.

For a better understanding and implementation, the present invention will be described in detail below in combination with accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural schematic diagram of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in Embodiment 1 of the present invention.

FIG. 2 is an SEM sectional view of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating prepared in Embodiment 1 of the present invention.

FIG. 3 is a structural schematic diagram of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in Embodiment 2 of the present invention.

FIG. 4 is an SEM sectional view of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating prepared in Embodiment 2 of the present invention.

DETAILED DESCRIPTION

For a further description of technical means adopted for achieving the objective of the present invention and achieved technical effects, a description will be given below on the features and specific embodiments of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler and a preparation method proposed in the present invention in combination with embodiments and accompanying drawings below, and the detailed description is as follows.

The high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention comprises a substrate layer, a primer layer and an anticorrosion coating which are stacked in sequence from bottom to top. The anticorrosion coating is an Inconel625-NiCrTiAlSi/La₂O₃ composite coating, and the composite coating is mixed by Inconel625 and NiCrTiAlSi/La₂O₃ in proportion. The substrate layer is any of carbon steel and alloy steel. The primer layer is a NiAl alloy layer with a preferable thickness of 80-100 μm. The anticorrosion coating has a preferable thickness of 0.3-0.5 mm.

The method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention comprises the following steps:

(1) uniformly mixing Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder in proportion to obtain composite powder; (2) grinding evenly the composite powder obtained in the step (1) to obtain spherical composite powder and drying the spherical composite powder; (3) cleaning and roughening the surface of a heating surface of a waste incinerator; (4) adopting a thermal spraying technique to spray a primer layer on the surface of the heating surface; (5) adopting a thermal spraying technique to spray the spherical composite powder obtained in the step (2) on the primer layer in the step (4); and (6) cooling to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

Wherein the mass percentage of the Inconel625 alloy powder and the NiCrTiAlSi/La₂O₃ alloy powder in the step (1) is preferably 85%-90% and 10%-15%, respectively.

The spherical composite powder obtained in the step (2) has a particle size of 25-53 μm, and the spherical composite powder is obtained through ball milling the composite powder obtained in the step (1). The spherical composite powder in the step (2) is dried preferably at a temperature of 100-150° C. to remove moisture.

The step (3) comprises such treatment of rust removal, oil removal and sand blasting on the heating surface of the waste incinerator, to remove foreign matters on the surface and to roughen the surface.

In the step (4), the primer layer is a NiAl alloy layer, and the average spraying thickness of the NiAl alloy layer is 80-100 μm. In the step (5), the average spraying thickness of the spherical composite powder coating is 0.3-0.5 mm.

The thermal spraying technique in the step (4) and step (5) is a supersonic flame spraying technique or a supersonic plasma spraying technique.

Technical parameters of the supersonic flame spraying technique are preferably as follows: the pressure of fuel gas propane is 0.35-0.45 MPa, the flow of combustion-supporting gas oxygen is 1600-1800 SCFH, the flow of kerosene is 5-7 GPH, the flow of carrier gas is 20-25 SCFH, the powder feed rate is 50-70 g/min, the gun distance is 300-400 mm, and the linear velocity is 400-600 mm/s.

Embodiment 1

Please refer to FIG. 1 which is a structural schematic diagram of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present embodiment. The coating comprises a substrate layer 11, a primer layer 12 and an anticorrosion coating 13 which are stacked in sequence from bottom to top. The anticorrosion coating 13 is an Inconel625-NiCrTiAlSi/La₂O₃ composite coating, and the composite coating is mixed by Inconel625 and NiCrTiAlSi/La₂O₃ in a mass percentage of 90% and 10% respectively. The substrate layer 11 is any of carbon steel and alloy steel. The primer layer 12 is a NiAl alloy layer with a thickness of 80-100 μm. The anticorrosion coating 13 has a thickness of 0.3-0.5 mm.

The method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention comprises the following steps:

(1) uniformly mixing Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder in proportion to obtain composite powder.

Specifically, Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder are weighed according to a mass percentage of 90% and 10% respectively and then are mixed uniformly, and then Inconel625-NiCrTiAlSi/La₂O₃ composite powder is prepared through a water atomization or gas atomization technique. Wherein the NiCrTiAlSi/La₂O₃ alloy powder is composed of the following components in mass percentage: 80-85% of Ni, 5-8% of Cr, 3-8% of Ti, 3-8% of Al, 1-3% of Si and 2-4% of La₂O₃.

(2) grinding evenly the composite powder obtained in the step (1) to obtain spherical composite powder and drying the spherical composite powder.

The composite powder obtained in the step (1) is grinded evenly through ball milling, to prepare spherical composite powder with an average particle size of 25-53 μm. The spherical composite powder is dried at 100-150° C. with a dryer to remove moisture.

(3) cleaning and roughening the surface of a heating surface of a waste incinerator.

In the present embodiment, the heating surface of the waste incinerator adopts No. 20 carbon steel as a base material, and the surface of No. 20 carbon steel is subjected to rust removal, oil removal and sand blasting, and the surface of the base material is roughened.

(4) adopting a thermal spraying technique to spray a primer layer on the surface of the heating surface.

In the present embodiment, the primer layer adopts NiAl alloy powder, and parameters of the thermal spraying technique are as follows: the pressure of fuel gas propane is 0.40 MPa, the flow of combustion-supporting gas oxygen is 1700 SCFH, the flow of kerosene is SGPH, the flow of carrier gas is 22 SCFH, the powder feed rate is 60 g/min, the gun distance is 350 mm, the linear velocity is 500 mm/s, and spraying is conducted for 4 times.

(5) adopting a thermal spraying technique to spray the spherical composite powder obtained in the step (2) on the primer layer in the step (4).

In the present embodiment, parameters of the thermal spraying technique are as follows: the pressure of fuel gas propane is 0.45 MPa, the flow of combustion-supporting gas oxygen is 1700 SCFH, the flow of kerosene is 6 GPH, the flow of carrier gas is 23 SCFH, the powder feed rate is 60 g/min, the gun distance is 350 mm, the linear velocity is 500 mm/s, and spraying is conducted for 12 times.

(6) cooling to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

The sprayed heating surface of the waste incinerator provided with a coating is cooled naturally through air cooling, to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

Please refer to FIG. 2 which is an SEM sectional view of a coating which is prepared through the method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler. The composite coating covers on the primer layer closely, indicating that the composite coating and the primer layer have a favorable binding force, thereby being capable of preventing chlorine from corroding base materials.

A high temperature chloride corrosion resistant coating prepared through the preparation method in the present invention is corroded for 100 hours at 900° C. in mixed molten salt which is composed of KCl, K₂SO₄ and Na₂SO₄ at a mass fraction of 10%, 10% and 80% respectively, wherein the thickness of a corrosion layer is about 2.6 μm, and no falling off of corrosion products is observed on the surface of the coating. In the prior art, as to a 45CT coating adopting supersonic spraying, under the same corrosion conditions, the thickness of the corrosion layer reaches 10.4 μm, and falling off of partial corrosion products is observed, indicating that compared with the coating in the prior art, the coating in the present invention has a more favorable corrosion resistance property at a high chloride environment, and can satisfy requirements of a heating surface of the existing waste incinerator on the corrosion property of the coating materials.

Compared with the prior art, as to the method for preparing the high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention, the Inconel625-NiCrTiAlSi/La₂O₃ composite coating on the NiAl primer layer can dramatically improve the binding force between the coating and the substrate layer; the adding of a rare element La₂O₃ can purify a grain boundary of the coating in the coating, thereby strengthening the grain boundary, promoting formation of an oxide film, changing the morphology of the coating, refining grains, and improving high temperature corrosion resistance and oxidation resistance. The composite coating composed of Inconel625 alloy and NiCrTiAlSi/La₂O₃ alloy possesses the functions of multiple alloy coatings, thereby further improving capability of resistance to high temperature erosion of the boiler.

Beneficial effects in the three aspects have a positive effect in protection of a waste incineration boiler under severe working conditions, thereby prolonging service life of the boiler and saving cost.

Embodiment 2

Please refer to FIG. 3 which is a structural schematic diagram of a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present embodiment. The coating comprises a substrate layer 21, a primer layer 22 and an anticorrosion coating 23 which are stacked in sequence from bottom to top. The anticorrosion coating 23 is an Inconel625-NiCrTiAlSi/La₂O₃ composite coating, and the composite coating is mixed by Inconel625 and NiCrTiAlSi/La₂O₃ in a mass percentage of 85% and 15% respectively. The substrate layer 21 is any of carbon steel and alloy steel. The primer layer 22 is a NiAl alloy layer with a thickness of 80-100 μm. The anticorrosion coating 23 has a thickness of 0.3-0.5 mm.

The method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention comprises the following steps:

(1) uniformly mixing Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder in proportion to obtain composite powder.

Specifically, Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder are weighed according to a mass percentage of 85% and 15% respectively and then are mixed uniformly, and then Inconel625-NiCrTiAlSi/La₂O₃ composite powder is prepared through a water atomization or gas atomization technique. Wherein the NiCrTiAlSi/La₂O₃ alloy powder is composed of the following components in mass percentage: 80-85% of Ni, 5-8% of Cr, 3-8% of Ti, 3-8% of Al, 1-3% of Si and 2-4% of La₂O₃.

(2) grinding evenly the composite powder obtained in the step (1) to obtain spherical composite powder and drying the spherical composite powder.

The composite powder obtained in the step (1) is grinded evenly through ball milling, to prepare spherical composite powder with an average particle size of 25-53 μm. The spherical composite powder is dried at 120° C. with a dryer to remove moisture.

(3) cleaning and roughening the surface of a heating surface of a waste incinerator.

In the present embodiment, the heating surface of the waste incinerator adopts No. 20 carbon steel as a base material, and the surface of No. 20 carbon steel is subjected to rust removal, oil removal and sand blasting, and the surface of the base material is roughened. The base material is not limited hereto, and can also be carbon steel and alloy steel.

(4) adopting a thermal spraying technique to spray a primer layer on the surface of the heating surface.

In the present embodiment, the primer layer adopts NiAl alloy powder, and parameters of the thermal spraying technique are as follows: the pressure of fuel gas propane is 0.40 MPa, the flow of combustion-supporting gas oxygen is 1700 SCFH, the flow of kerosene is SGPH, the flow of carrier gas is 22 SCFH, the powder feed rate is 60 g/min, the gun distance is 350 mm, the linear velocity is 500 mm/s, and spraying is conducted for 4 times.

(5) adopting a thermal spraying technique to spray the spherical composite powder obtained in the step (2) on the primer layer in the step (4).

In the present embodiment, parameters of the thermal spraying technique are as follows:

the pressure of fuel gas propane is 0.45 MPa, the flow of combustion-supporting gas oxygen is 1800 SCFH, the flow of kerosene is 6.5 GPH, the flow of carrier gas is 23 SCFH, the powder feed rate is 60 g/min, the gun distance is 350 mm, the linear velocity is 500 mm/s, and spraying is conducted for 12 times.

(6) cooling to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

The sprayed heating surface of the waste incinerator provided with a coating is cooled naturally through air cooling, to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator.

Please refer to FIG. 4 which is an SEM sectional view of a coating which is prepared through the method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler. The composite coating covers on the primer layer closely, indicating that the composite coating and the primer layer have a favorable binding force, thereby being capable of preventing chloride from corroding base materials.

A high temperature chloride corrosion resistant coating prepared through the preparation method in the present invention is corroded for 100 hours at 900° C. in mixed molten salt which is composed of KCl, K₂SO₄ and Na₂SO₄ at a mass fraction of 10%, 10% and 80% respectively, wherein the thickness of a corrosion layer is about 2.8 μm, and no falling off of corrosion products is observed on the surface of the coating. In the prior art, as to a 45CT coating adopting supersonic spraying, under the same corrosion conditions, the thickness of the corrosion layer reaches 10.4μm, and falling off of partial corrosion products is observed, indicating that compared with the coating in the prior art, the coating in the present invention has a more favorable corrosion resistance property at a high chloride environment, and can satisfy requirements of a heating surface of the existing waste incinerator on the corrosion property of the coating materials.

Compared with the prior art, as to the method for preparing the high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler in the present invention, the Inconel625-NiCrTiAlSi/La₂O₃ composite coating on the NiAl primer layer can dramatically improve the binding force between the coating and the substrate layer; the adding of a rare element La₂O₃ can purify a grain boundary of the coating in the coating, thereby strengthening the grain boundary, promoting formation of an oxide film, changing the morphology of the coating, refining grains, and improving high temperature corrosion resistance and oxidation resistance. The composite coating composed of

Inconel625 alloy and NiCrTiAlSi/La₂O₃ alloy possesses the functions of multiple alloy coatings, thereby further improving capability of resistance to high temperature erosion of the boiler. Beneficial effects in the three aspects have a positive effect in protection of a waste incineration boiler under severe working conditions, thereby prolonging service life of the boiler and saving cost.

The present invention is not limited to the above embodiments. If various modifications or variations made to the present invention do not depart from the spirit and scope of the present invention, and if these modifications and variations fall within the scope of the claims and equivalent techniques of the present invention, then the present invention also intends to encompass these modifications and variations. 

1. A method for preparing a high temperature chloride corrosion resistant NiCrTiAlSi/La₂O₃ coating at a flue gas side of a waste incineration power generating boiler, comprising the following steps: (1) uniformly mixing Inconel625 alloy powder and NiCrTiAlSi/La₂O₃ alloy powder in proportion of (85%-90%):(10%-15%) in mass percentage to obtain composite powder, wherein the NiCrTiAlSi/La₂O₃ alloy powder is composed of following components in mass percentage: 80-85% of Ni, 5-8% of Cr, 3-8% of Ti, 3-8% of Al, 1-3% of Si and 2-4% of La₂O; (2) grinding evenly the composite powder obtained in the step (1) to obtain spherical composite powder and drying the spherical composite powder; (3) cleaning and roughening a surface of a heating surface of a waste incinerator; (4) adopting a thermal spraying technique to spray a primer layer on the surface of the heating surface, wherein the primer layer is a NiAl alloy layer; (5) adopting a thermal spraying technique to spray the spherical composite powder obtained in the step (2) on the primer layer in the step (4); and (6) cooling to obtain a high temperature chloride corrosion resistant coating of the heating surface of the waste incinerator. 2-4. (canceled)
 5. The method of claim 1, wherein in the step (4), the primer layer has a spraying thickness of 80-100 μm; and in the step (5), the spherical composite powder has a spraying thickness of 0.3-0.5 mm.
 6. The method of claim 1, wherein the spherical composite powder obtained in the step (2) has a particle size of 25-53 μm, and the spherical composite powder is obtained through ball milling the composite powder obtained in the step (1).
 7. The method of claim 1, wherein the thermal spraying technique in the step (4) and step (5) is a supersonic flame spraying technique or a supersonic plasma spraying technique.
 8. The method of claim 7, wherein the thermal spraying technique in the step (4) and step (5) is a supersonic flame spraying technique, and technical parameters of the supersonic flame spraying technique are as follows: a pressure of fuel gas propane is 0.35-0.45 MPa, a flow of combustion-supporting gas oxygen is 1600-1800 SCFH, a flow of kerosene is 5-7 GPH, a flow of carrier gas is 20-25 SCFH, a powder feed rate is 50-70 g/min, a gun distance is 300-400 mm, and a linear velocity is 400-600 mm/s.
 9. The method of claim 8, wherein in the step (4), the primer layer is sprayed for 4 times; and in the step (5), the spherical composite powder is sprayed for 12 times. 10-15. (canceled) 